Methylated derivatives of hydrazine



United States Patent 3,102 144 METHYLATED DERlVA'llVES 0F HYDRAZINE David Horvitz, Hyattsville, Mei, assignor, by mesne assignments, to FMC Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Sept. 15, 1954, Ser. No. 456,317 1 Claim. (Cl. 269-583) This invention relates to the production of methylated derivatives of hydrazine, to mixtures and solutions containing such methylated derivatives, and to methods of obtaining substantial yields of preferred products.

Among the objects of the present invention is the production of methylated derivatives of hydrazine from hydrazine, lower methylated derivatives of hydrazine, sulfates of hydrazine and lower methylated hydrazines, and any desired mixtures or solutions thereof.

Other objects include methods of control to accentuate the extent of methylation desired.

Further objects includemethods of recovery of the desired derivatives.

Still further objects and advantages of the present invention will appear from the more detailed description set forth below, it being understood that such more detailed description is given by way of illustration and explanation only and not by way of limitation since various changes therein may be made by :those skilled in the art without departing from the scope and spirit of the present invention.

In accordance with the present invention, it has been found that hydrazine and its various derivatives may be methylated under controllable conditions to give substantial yields of methylated hydrazines by the use of dimethylsulfate, methyl sulfuric acid, or an alkali methyl sulfate. For example, hydrazine may be reacted with a methylating sulphate, such as dimethylsulfate, methyl acid sulphate, and alkali methyl sulphate, and depending on the relative ratio of materials used and the conditions under which the reaction is conducted, there can be obtained differing quantities of the various hydrazine derivatives; i.e., methylhydrazine, uns-dimethylhydrazine, symmetrical dimethylhydrazine, itrirnethylhydrazine and the quaternary salts thereof. In general, it is difficult to get exclusively one derivative, but the reaction maybe performed so that a particular desired derivative is predominant. The individual derivatives can be isolated and purified as desired; for example, by fractional distillation or by azeotropic distillation.

The reaction of the methylating agent with hydrazine or with methylated hydrazines may be performed in a variety of ways. It may be performed in a solvent such as alcohol, e.g. ethanol, isopropanol, ethylene glycol or other glycols; in a diluent which is immiscible with hydrazine but miscible with the methylating agent such as toluene, xylene or other hydrocarbons or ethers or alcoholic ethers or other inert diluents; or water which is miscible with hydrazine but not with dimethylsulfate, may be used; or combinations of these solvents or diluents. Alkali or alkaline earth oxides, hydroxides or carbonates can be used in appropriate equivalent quantities. On the other hand, it is found also possible to perform this reaction without any solvents and without any fixed caustic present, and in effect, this is the more desirable method.

In the preferred process the methylating agent is added with stirring and cooling to the anhydrous hydrazine (commercial grades may vary from 90 to 100%, all concentrations being useable in this process). During this reaction, cooling is desirably applied to absorb the considerable heat which is evolved. The reaction temperature is commonly maintained at about 30 C. but the temperature may vary, for example, from below 0 up to 3 1%,144 Patented Aug. 27, 1963 ice 135 C. If performed in the upper temperature range, the products of reaction distill simultaneously with the input of methylating agent. In general, it is preferable to complete the admixture of the desired molar proportions of methylating agent and hydrazine before this distillation commences. Consequently, in a batch-size process it is preferable to add all of the methylating agent to the hydrazine or methylated hydrazines art a lower temperature range, such as 30 C., before the next stage (i.e., the distillation stage) is reached. In a continuous operation it is possible to mix continuously the correct molar proportions of methylarting agents and hydrazine and to allow the temperature to rise immediately to the distillation stage. The reaction mixture produced at the lower temperature is capable, of undergoing an exothermic reaction and indeed does so even if allowed to stand at ambient temperature. In the latter case, the reaction proceeds to completion slowly in a matter of many hours. If the heat generated during this reaction is not dissipated, it will cause a general increase in the temperature of the mass until a point is reached where the reaction proceeds at a very rapid rate. This reaction temperature is approximately C. It is customarily preferable to take the reaction mixture when it has been prepared at the lower temperature range such as approximately 30 C. and to add a small quantity to a reaction vessel; heat this material to about C. to insure that the exothermic stage of the reaction has commenced at a rapid rate and then add the remaining reaction solution continuously to this vessel at the same time that distillation products are taken ofi. For the most part, no heat to be added to this reaction to maintain the temperature since it is exothermic and the temperature is controlled primarily by the rate at which the reaction solution is added to the vessel. Occasionally it may be necessary to apply heat to accelerate the reaction. The product which distills may be a varying mixture of the different methylhydrazines depending upon which molar ratio of reactants, such as hydrazine to methylating agent was used. The distillation product can be fed into a column directly to take off by fractionation the products in proper sequence depending upon their boiling points. Where solvents, such as isopropyl alcohol or toluene have been used, special separation processes may be used, depending on the amount and kind of solvent employed and on the particular hydrazine derivatives which have been formed. However, the yields and relative quantity of product obtained are similar whether a solvent or a diluent has been used. The amount of solvent or diluent used therefore is not critical and it serves primarily as a heat dissipating agent.

The reaction mass which is left behind after the exothermic distillation when dimethylsulfate has been used as the methylatiug agent, consists primarily of a solid which contains two moles of hydrazine or methylated hydrazine to one mole of methyl acid sulfate, although this is not intended to represent the actual chemical constitution of this material. There may also be present some excess hydrazine or methylated hydrazine.

Depending on the molar ratios of hydrazine to methylating sulphate such as dimetbylsulfate, the first distill-ate contains differing proportions of derivatives. For example, if the molar ratio of hydrazine to dimethylsulfate is equal to 3.75, then the resulting distilled product contains about 1.5 parts by weight of methylhydrazine and one part by weight of unsymmetrical dimethylhydrazine, as well as 1 to 3% by weight of symmetrical dimethylhydrazine and trimethylhydrazine. If the molar ratio of hydrazine to dimethylsulfate is three to one, then the distilled product contains approximately 1.4- parts of uns-dirnethylhydrazine to one part of methylhydrazine. In this case also there is 1 to 3% of symmetrical dimethylhydrato the boiling point of the mixture.

zinc and trimethylhydrazine. At a molar ratio of 2.5 to l, the proportion of unsymmetrical dimethyl'hydrazine to methylhydrazine is about 3.l to 1. Furthermore, about of the weight of methylated products in the distillate is trimethylhydrazine. With lower mole ratios the tendency towards higher degree of methylation of the hydra zine molecule increases, but at the same time the tendency toward formation of quaternary salts also increases. Un-' less quaternary salt is a desired product, its formation results in loss of useful hydrazine and dimethylsulfate. It is also possible to react the dimethylsul fiate with already methylated hydrazines or their mixtures with hydrazine. For example, a mixture of methylhydrazine with hydrazine, when treated wit-h dimethylsulfate, gives a much higher proportion "of unsymmetrical dimethylhydrazine; treatment of symmetrical dimethylhydrazine with dimethylsulfiate gives a hignyield of trimethylhydrazine. The relative quantities of materials given in this paragraph represent "only the materials obtained from the first distillation during the exothermic phase. The products that are obtained at a molarratio of 3.75 to 1 represent a 100% yield based on the number of methyl groups introduced into the hydrazine molecule and assuming only one methyl group available in this'stage per molecule of dimethylsulfate. On the same basis it is round that for a molar ratio of3 to 1 about 92% of the available methyl groups .arefound in the Volatile methylated products; at a molar ratio of 2.75 to 1 about 80% are used; and at 2.5 to 1 about 63% are used. The methyl groups not rfiound in the volatile products are probably present as quaternary salts. The residue refer-red to previously Which contains the molar proportions of approximately 2 moles of hydrazine to one mole of methyl acid sulfate is treated by adding an alkali or alkaline earth oxide or hydroxide such as sodium hydroxide or calcium hydroxide to it While maintaining a temperature from 85 C. to 100 -C. The residue is a solid which is found to melt at about 85 C. but when some caustic has reacted with it,

the reaction performed at temperatures ranging from ambient to the boiling point.

Other diluents or solvents, such as alcohols, hydrocarbons or ethers, may be used and the caustic may be added as an aqueous or alcoholic solution, or as a solid at temperatures ranging from approximately room temperature At temperatures below 85 C. the solidcaustic goes into reaction very slowly, but :above 85 C., the reaction proceedsreadily and with some vigor. Two moles of caustic are desirably added for every mole of sulfate that is present, although it is sometimes desirable to add less than this amount of caustic, as further explained below.

The further treatment of the residue with alkali serves to promote further methyl-ation by use of the second methyl group of thedimethylsulfate molecule. It also permits recovery of excess hydrazine. At this stage also it is possible to obtain formation of differing proportions of methylated products, depending on the manner in which the reaction is performed. It the solid lalkali is added to the residue at 85 C. to 100 C. in amount equivalent to the sulfate present, then approximately 0.25 to 0.30 mole of met-hylhydrazine per mole of dimethylsultion' of the caustic. In this way a much higher percentage.

late that was used in the reaction, is obtained; about 0.2 I

to 0.3 mole of quaternary salt per mole of dimethylsul fate; and the remainder of the hydrazine used in the reaction is recoverable as such. When the reaction is conductedin this manner, a larger portion of the methyl groups become tied up as quaternary salt. However, if less than an equivalent quantity of caustic is used it is possible to obtain greater quantities of unsymmetrical dimethylhydrazine and methylhydrazine, and less quaternary salt formation. Another method is to distill off methylated products as they are formed during the addiof volatile methylated hydrazine products is obtained and less quaternary salt is formed.

The vaforementioned reaction can be performed also by adding the methylating agent to hydram'ne at elevated temperature and distilling oil methylated products as they are formed. It is preferable in this case to use a fractionating column and maintain reflux and take-off at such rate as to take off the desired product. This method is most useful for producing a maximum unsymmetrical dimethylhydrazine which boils at 63 64 C. This procedure can be used with or without added alkali, although it is preferable without the alkali, because at this stage the alkali saponifies an appreciable portion of the methylsulfate to methanol. On the other hand, the alkali treatment to utilize the second methyl group as described pre- -viously, does not saponify the methyl group.

It is found that the same principles and procedures apply whether dimethylsulfiate is used or methylsulfuric acid or an alkali methylsulfate, such as sodium methylsul fate. There is a difference in that no second methyl group is involved and subsequent treatment of the residue is primarily to recover excess hydrazine or methylated hydrazine, but not to induce further methylation.

A modification of the methylationreaction which is useful, in that it produces relatively large quantities of methylhydrazine and permits easier recovery of excess hydrazine, is the following:

Dihydrazine sulfate is dissolved in a minimum of water and one mole (per mole of the dihydrazine sulfate) of dimethylsulfiate is added over a period of time. During this addition, monohydrazine sulfate which is relatively insoluble in water separates out almost quantitatively as a crystalline White solid. When all the dimethylsul-fate has been added, the solution is filtered, and the filtrate is added to a hot slurry of solid alkali or alkaline earth hydroxide in water. At least two equivalents of caustic are used for every mole of dimethylsulfate which was used in the initial reaction; in addition excess caustic may be used to facilitate the distillation of the methylated Under these conditions some methanol is also produced because of saponification of the di-methylsulfate. The relative proportions of dimethylsulfate to dihydrazine sulfate may be varied from that given. In addition excess hydrazine above that in the dihydrazine sulfatemay be used. The excess hydrazine may be added before the addition of the rnethylsulfiate, or to the filtrate after filtering olf the monohydrazine sulfate. The monohydrazine sulfate is used for the next reaction by simply adding another equivalent of hydrazine.

It is also possible to add an equivalent of methyl-hydrazine (or other methylated hydrazine product) to the monohydrazine sulfate in order to produce more highly methylated products. The reaction intermediate obtained as filtrate after filtering off the monohydrazine sulfate can he treated with alkali as already indicated or may be treated by adding caustic to it and then distilling; or distillation may go on while caustic is added to it. These variations of technique result in diiierentrelative and absolute amounts of the various methylated hydrazines, and the method chosen is determined by the products particularly desired. Another variation of this method involves a similar system using a non-aqueous system, such as ethylene-glycol, glycerol, methanol; the reaction is performed in similar fiashion.

The volatile products, methylhydrazine, unsdimethylhydrazine, sym-dimethylhyd-razine, trimethylhydrazine, and excess hydrazine are readily separated from each other in pure form by fractionation in an efficient distilling column. Even from large quantities of Water all of these products,

except hydrazine itself, can be distilled directly out as the pure, anhydrous compounds. In the prior art it has been commonly accepted that isolation of these products in the anhydrous state required special treatment, with dehydrating types of chemicals, such as sodium hydroxide, potassium hydroxide or barium oxide. However, it has been found that these products form no azeotrope with water or with each other and can be distilled directly oi as the pure products by efiicient fractionation. The lowest boiling fraction is trimethylhydrazine which boils at 6061 C.; then follows unsymmetrical dirnethylhydrazine at 63-64 C.; then symmetrical dimethylhydrazine at 80-81 C.; and finally methylhydrazine at 87-88 C. The most difficult to separate from each other are trimethylhydrazine and unsymmetrical dimethylhydrazine which have boiling points very close to each other. Ultimate separation is possible by fractionation,

but it requires a high fractioning efficiency. A convenient method for separating them is to add enough methanol to form an azeotrope with the unsymmetrical dirnethylhydrazine. This aseotrope boils at about 7173 C., contains about 55% unsymmetrical dimethylhydrazine and because of the higher boiling point is easily separated from the trimethylhydrazine. The first distillate is often found to produce slight amounts of colored products on fractionation which tend to color the various fractions. This difficulty is taken care of by adding a small quantity of an alkaline reagent, such as alkali or alkaline earth oxide, hydroxide or carbonate before fractionation. For certain uses mixtures of these methylated hydrazines are valuable and it is then desirable to perform the reaction with those mole ratios and conditions which give the sought for proportions of products. If the proportion is correct, it is suflicient to distill the mixtures without rectification. Mixtures of this sort, as well as the individual compounds, are useful as fuels for jet propulsion. Certain mixtures, particularly those of methylhydrazine, uns-dimethylhydrazine, trimethylhydrazine and hydrazine, where two or more of these named components may be present in varying proportions, have advantages in certain cases with respect to cost, freezing point, boiling point, density, hypergolic ignitibility, and other properties.

Example I 5760 grams of anhydrous hydrazine were placed in a reaction flask, and to it with stirring and cooling, were added 6050 grams of dimethylsulfate. An ice-salt bath was used for cooling and the temperature in the reaction mixture was maintained between 20 and 30 C. To another flask equipped with stirrer and condenser for down distillation, about 150 to 200 rnls. of the reaction solution were added and brought to a temperature of approximately 115 by external heating. Distillation of a liquid commenced and then the remainder of the initial reaction solution was added at such rate that the temperature in the reaction mixture remained between 125 and 135 C. At the same time product continuously distilled over. When the reaction was finished, the distillate was fractionated in a column and the following products obtained out of the mixture: about 1.64 pounds of unsymmetrical dirnethylhydrazine (HP. 63 to 64 C.); 2.45 pounds of rnethylhydrazine (B.P. 87 to 88 C.); 0.12 pound of symmetrical dirnethylhydrazine (B.P. 80 to 81 C.); 0.04 pound of trirnethylhydrazine (13.1. 60 to 61 C.); and 0.66 pound :of hydrazine. The fractionation was performed in a column which had 15 to 20 theoretical plates. A forerun between 60 and 63 C. contained the trimethylhydrazine plus some unsymmetrical dimethylhydrazine. This forerun was further frac tionated in a small column; it required two further fractionations to obtain the pure trimethylhydrazine. In the big column uns-dimethylhydrazine was taken off between 632 and 638 C. A center-cut was taken 0E between 638 and 873 C. Finally the methylhydrazine was taken off between 873 C. and 878 C. The centercut was separately fractionated in a small column to give uns-dimethylhydrazine, symmetrical dimethylhydrazine (from C. to 81 C.) and methylhydrazine. To get pure symmetrical dimethylhydrazine the 80 to 81 C.

Example 11 A reaction was performed as in Example 1, except that 5120 grams of hydrazine were used and 6720 grams of dirrrethylsulfate. The first distillate was found to contain the following: 2.07 pounds of uns-dimethylhydrazine; 1.50 pounds of methylhydrazine; 0.12 pound of symmetrical dimethylhydrazine; 0.08 pound of trimethylhydrazine; and 0.20 pound of hydrazine. The residue remaining after the exothermic distillation was treated with 3300 grams of sodium hydroxide (only 77% of the equivalent amount). Distillation of the resulting product gave about 0.6 pound of unsymmetrical dimethylhydrazine, about 2.6 pounds of methylhydrazine and about 3.1 pounds of hydrazine.

Example 111 7560 grams of dimethylsulfiate were reacted with 4800 grams of anhydrous hydrazine, as described in the preyious examples. The first distill-ate was found to contain the following: 1.78 pounds of unsymmetrical dirnethylhydrazine; 0.58 pound of methylhydrazine; 0.27 pound of tn'methylhydrazine; negligible quantities of symmetrical dimethylhydrazine and hydrazine. The residue obtained after the first distillation was treated with 4800 grams of solid sodium hydroxide which was added while the mixture was heated and allowed to distill off part of the resulting products through a short fractionating column. The resulting distillate was found to contain 1.5 pounds of unsymmetrical dimethylhydrazine; 3.2 pounds of methylhydrazirre and 3.8 pounds of hydrazine.

Example IV 576 grams of anhydrous hydrazine were diluted with one liter of isopropanol and to this solution were added 540 grams .of potassium hydroxide. To this mixture, with cooling and stirring, were added 608 grams of dirnethylsulfate. After all the dimethylsulfate had been introduced, the reaction mixture was heated to distill off the product. When the temperature reached approximately 85 to C., an exothermic reaction set in and cooling had to be applied to control the distillation. The distillate consisted of a mixture of isopropanol together with the methylated hydrazines and some excess hydrazine. Sulfuric acid was added to the distillate, and it was evaporated almost to dryness. The residue was treated with 50% sodium hydroxide solution in water and then fractionated. The final product was found to contain approximately 70 grams of unsymmetrical dirnethylhydrazine, grams of methylhydrazine and 325. grams of hydrazine. Symmetrical dimethylhydrazine and trimethylhydrazine were present in minor quantities only.

Example V 576 grams of anhydrous hydrazine were diluted with 500 mls. of toluene, with which it is immiscible, and 608 grams of dimethylsulfate were added with cooling and stirring. After the dimethylsulfate had been added, it was found that the toluene was present as an immiscible layer on top of the reaction mixture. The toluene layer was removed and the remainder was treated as in Example I, both with respect to the first distillation and then treatment with caustic. The products obtained by fraction-ation were in about the same proportion as obtained in Example I.

Example VI A reaction was performed as in Example V, except that 576 mls. of water were used as solvent instead of the toluene. The products obtained were in approximately the same relative proportions, but the over-all yield was about 10% lower.

Example VII 150 grams of potassium methylsulfate were added slowly with stirring and cooling to 64 grams of anhydrous hydrazine. From this mixture a distillate was obtained which contained about grams of unsymmetrical dimethylhydrazine and 16 grams of methylhydrazine. Some quaternary salt was also found in this reaction because of the low molar ratio of hydrazine to potassium methylsulfate.

Example VIII 150 grams of potassium methylsulfate were added with cooling and stirring to 92 grams of methylhydrazine. The distillate from this reaction was found to contain about 22 grams of unsymmetrical dimethylhydrazine and '11 grams of methylhydrazine.

Example IX Example X 63 grams of dimethylsulfate were added with stirring and cooling to 120 grams of symmetrical dirnethylhydrazine. The distillate from this product was found to contain about 41 grams of trimethylhydrazine and 31 grams of symmetrical dimethylhydrazine. The distillation residue was treated with 44 grams of sodium hydroxide and then distilled to give about grams of symmetrical dimethylhydrazine containing 1 or 2 grams of trimethylhydrazine.

Example X] To a mixture of 128 grams of hydrazine and 552 grams of methylhydrazine were added 504.5 grams of dimethylsulfate. The distill-ate from this reaction containing 187 grams of unsymmetrical dimethylhydrazine and 215 grams of methylhydrazine. From the residue treated with sodium hydroxide were obtained approximately 124 grams of hydrazine and 85 grams of methylhydrazine as,

distillate. Remaining in the residue Were approximately 2 mols ortrimethylhydrazinium quaternary salt.

Example XII 975 grams of monohydrazine sulfate were treated with 240 grams of hydrazine, plus enough water to bring the resulting dihydrazine sulfate into solution. To this solution were now added 945 grams of dimethylsulfate, during which time the reaction mixture was stirred and maintained in a temperature range of to C. During the course of the addition, monohydrazine sulfate precipitated out of the solution as a white crystalline solid. At the end of the reaction the mixture was filtered to give an almost quantitative return of the monohydnazine sulfate used at the commencement of the reaction. The filtrate was then dropped upon a stirred slurry of 1725 grams of solid sodium hydroxide to which had been added 250 mls. of 50% sodium hydroxide solution in water. At the same time the reaction flask was heated so that the product distilled simultaneously as the filtrate was added to the caustic. About 750 mls. of distillate were obtained and fractionated. Found in the separate fractions were approximately 71 grams of un symmetrical dimethylhydnazine, 30 grams of trimethylhydrazine, 34 grams of methanol (obtained as an azeotrope-with unsymmetrical dimethy lhydrazine; this azeotrope boils at 71-73 C.), and grams of methylhydrazine.

Example XIII An apparatus was arranged to permit hydrazine and dimethylsulfate to flow continuously at controlled rates into the bottom of a small, narrow, cooled chamber equipped with stirrer. The mixture formed therein could overflow out of the top and into the bottom of a heated, packed column. This column was so arranged that distillate could be condensed at the top and drawn oif, while the hot, molten residue could overflow into another vessel. This apparatus was employed'to conduct a continu ous reaction between hydrazine and dimethylsulfate. In an experiment in which these reactants were fed into the system at a molar ratio of 3.75 moles of hydrazine to 1 mole of dimethylsulfate, the distillate was found to contain approximately the same relative proportions and yields as obtained in Example I. The residue was treated as in Example I with similar results.

Having thus set forth my invention, I claim:

The method of producing methylated compounds of hydrazine which comprises reacting hydrazininm acid sulphate with an equivalent amount of a hydrazine in which there are not more than two su-bstituent groups, each being methyl in the presence of water to form the neutral salt, reacting this solution with a methylating sulphate at a temperature of 60 to 85 C., filtering the solution, contacting the filtrate with a slurry of caustic alkali in water and distilling therefrom a product containing methylated hydrazines.

References Cited in the file of this patent FOREIGN PATENTS Great Britain Nov. 12, 1947 OTHER REFERENCES 

